Download "Java Core July: Память в Java. Лекция #4 (Часть 2)"

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CSS3 #13 Отображение элементов и вендорные префиксы (Display vs. Visibility, Vendor Prefixes)

CSS3 #13 Отображение элементов и вендорные префиксы (Display vs. Visibility, Vendor Prefixes)

Channel: webDev

лекция

ссылки

Java (Programming Language)

heap

stack

JMM

урок

Metaspace

Java (Software)

reference

хип

memory

java

PermGen

память

00:00:03

Where is it stored now, I wrote several

00:00:06

tests, but

00:00:08

they are not yet shared with you, they

00:00:11

will be

00:00:13

shared next time Well,

00:00:19

I will tell you the material now if I just have a local

00:00:22

variable and X is 12 and it is of a primitive

00:00:25

type, this means that there is a piece of memory in the stack

00:00:28

where it is written

00:00:32

12 if I have a reference type, for example, an

00:00:36

array of ixo masinto 12 is written there,

00:00:41

then I have a link to

00:00:44

some memory where it is written

00:00:51

12, from this it turns out yes to those

00:00:57

etofrmurova

00:00:58

vopros if I write and X ra 0 and y ra

00:01:06

1, then it is possible with a huge degree of

00:01:08

certainty according to the specification

00:01:10

of this, nothing is said, but any

00:01:13

normal 0 and 1 will lie next to each other in the

00:01:15

memory, it will most likely be adjacent

00:01:18

cells in the stack, then 4 bytes and the next 4

00:01:21

bytes are

00:01:23

0.1 if

00:01:32

well, I will make them into

00:01:40

arrays, that is more likely

00:01:45

Well, here it is no longer a fact that they will

00:01:49

lie

00:01:50

next to each other, most likely under the memory system,

00:01:53

if you select the arrays twice by contract,

00:01:55

select them next to each other, but it is not a fact, that is, it is not

00:01:58

possible. Oh, the links refer to

00:02:01

completely different completely different

00:02:03

places 0 is written in the pad,

00:02:08

but here, where, under the memory system,

00:02:11

select a new

00:02:15

array. Yes, what does this mean?

00:02:18

It affects when

00:02:21

high-performance

00:02:23

systems are designed, which is rare on Java, but in general, the

00:02:30

processor may have

00:02:32

some memory on my laptop, there is 8 GB,

00:02:36

but the processor and memory are two. different

00:02:37

microchips go from the processor to the

00:02:39

memory, there are somewhere around 200 clock cycles,

00:02:41

the processor, that is, my 2 GHz

00:02:44

drops sharply to 10 ml goes to the memory That is why the

00:02:47

processor has its

00:02:49

own small memory, it is called that there are

00:02:51

several kshey of the order of

00:02:54

256 directly on the processor part the transistor

00:02:57

will appear in memory, that's how it

00:03:00

went into memory. Read me

00:03:02

such and such a subsystem, which even

00:03:05

for the most part, things don't control.

00:03:16

when I go the second

00:03:22

time, if I have

00:03:28

an array of ra 0

00:03:32

2, then if I independently allocate And if I

00:03:35

use

00:03:37

x and then use the game, then it

00:03:40

may turn out that each time it costs

00:03:42

200 cycles

00:03:45

[applause] of

00:03:47

the processor if I write z0 ra Z1 ra, then

00:03:53

rather everything is it costs 200 clocks,

00:03:55

but it costs about

00:03:57

a clock so that the memory is stored in one place,

00:04:01

so when the processor went down

00:04:03

for a long time for the first time, it immediately grabbed a whole

00:04:06

portion of memory from there, and when I

00:04:08

go to cells that are standing next to each other, it

00:04:09

happens very

00:04:13

quickly, in principle, this is not

00:04:16

particularly important for the jarists First of all, we don't write

00:04:18

programs that generate millions of numbers per

00:04:19

second.

00:04:33

most likely they are located

00:04:36

sequentially, again in Java We

00:04:39

can't find this out in any way We can't in

00:04:41

the heat it is not said that the stack should be

00:04:42

continuous memory in the stack it is not said that

00:04:45

arrays are continuous memory but in any

00:04:47

normal implementation they make it so that it

00:04:50

finds

00:04:53

256,573

00:04:54

cells very quickly there is the address of the beginning of the array, they take in

00:04:57

the array that long long long 8 bytes multiply the

00:05:01

index by 8 bytes and get

00:05:04

an offset, however, in some

00:05:07

Android where the memory can be arranged

00:05:08

strangely, they will say that you have such a large

00:05:10

array, we cannot store it in one piece,

00:05:12

Mikrolinus It burns. I only

00:05:14

measure it by megabytes. And it may turn out that

00:05:17

in the end the array was cut into pieces,

00:05:18

but I’m not going to

00:05:22

kill it if I have an

00:05:25

object. Arrays and objects are literally

00:05:28

one and the same from the point of view of the location

00:05:30

in

00:05:33

[music]

00:05:34

memory. Well, let’s do it right away

00:05:42

let's look at the tests Now I wrote the

00:05:46

test today just from

00:05:53

memory if I have a

00:05:56

class h It will have X AND

00:06:02

Y I'll write h h =

00:06:06

h

00:06:11

0

00:06:18

usually give a class that

00:06:21

simply stores some data pointlessly called a

00:06:26

holder, in this case when I

00:06:30

declare Vot Yes, I declare a variable. I

00:06:33

declare something outside the scope of the method. This is not a

00:06:36

local variable. This is an object field. In

00:06:38

this case, it is initialized with zero.

00:06:41

Here it is possible to read and there will be

00:06:43

zero for numbers and zeros for references. Well,

00:06:48

for a boolean,

00:06:58

fse

00:07:03

is a

00:07:07

class, and now I am writing here. что

00:07:13

лр Хранитель ревен New Folder

00:07:17

01 вызваем

00:07:22

это

00:07:26

H

00:07:28

со

00:07:58

какой здесь будет ответ что напечает для компании

00:08:02

Please

00:08:04

don't

00:08:05

answer to create an intrigue sufficiently

00:08:25

[music] it's

00:08:28

complicated

00:08:40

object fields and array elements from the point

00:08:43

of view of placement in memory it's absolutely

00:08:45

one and the

00:08:47

same, that is, the difference is at the level of

00:08:49

language syntax, the elements of the array

00:08:52

must all be of the same type, I can't

00:08:54

say such an array where even is a

00:08:56

fleet And odd is strings

00:09:04

again

00:09:06

and here But I can't say, I want 500,000

00:09:11

fields, not all fields are individual Give everyone

00:09:15

a name, and from the point of view of memory it's

00:09:18

absolutely the same thing and the same

00:09:23

thing, look at me, H appears in me,

00:09:30

which

00:09:32

refers to the memory area

00:09:36

where the holder is somehow placed, an

00:09:39

instance

00:09:40

of holder since

00:09:43

ints are primitive types, they are

00:09:48

stored right

00:09:50

here, that is, here. It will be written that

00:09:53

0 and

00:09:54

1 when I call the

00:09:58

method I will order.

00:10:17

The same

00:10:21

object, I went through it and wrote 100 in Y.

00:10:25

I went through it and wrote 100 in Y,

00:10:31

and then I saved old in my local variable.

00:11:01

by serenky

00:11:04

Well, the value New holdolder -1 -2

00:11:07

is assigned but never

00:11:14

used in this case, that is,

00:11:16

some things seem to be more

00:11:18

sensitive than the language, a

00:11:21

number of things the compiler itself prohibits,

00:11:24

for example, if I do tn and

00:11:27

then it is equal to

00:11:32

it says that it will

00:11:35

never be completed, there is nothing

00:11:37

wrong and it is equal to

00:11:39

11 But this after the return means we will

00:11:42

definitely not get there and the compiler tells me

00:11:45

no, well, this is obvious stupidity, he is obliged to

00:11:48

prevent me from compiling it,

00:11:50

because somehow it is quite obvious that I

00:11:55

made a mistake. But

00:11:57

here I did not violate the specification of the language, I did

00:12:02

not do anything that is prohibited in the pdf,

00:12:05

however, mine is a

00:12:07

little bit more attentive, she

00:12:09

enlightened me, she highlighted this one,

00:12:12

she says it is not mandatory, this last

00:12:14

expression is all you leave the

00:12:16

method, so the language of this does not prohibit

00:12:20

doing it, but it advises that maybe you have

00:12:22

a mistake, that is, maybe you would have a

00:12:23

different logic, because it is so, everything is

00:12:25

so obvious, I will do it, and here the language

00:12:29

allows it, but it says Well, maybe you were

00:12:32

mistaken, for some reason you assign a value to a local argument to a

00:12:36

local variable

00:12:37

that you yourself never

00:12:39

use,

00:12:41

but it's not considered an error because

00:12:43

why it's not considered an error from the point of

00:12:45

view of language syntax, they said, what

00:12:47

if you do something in the constructor,

00:12:49

for example, create a

00:12:50

file, then of course the assignment can also be

00:12:53

an error.

00:12:59

you didn't save it anywhere

00:13:01

But suddenly you're in the constructor, that's what

00:13:03

he has, how do you create files,

00:13:05

send emails, there's something on the screen,

00:13:08

so we don't know what's there, we do

00:13:09

n't consider it a

00:13:11

mistake, they say, well, you're an

00:13:14

argon, Nika no more

00:13:16

you'll use the SES, I'll do it. Here's how

00:13:19

we'll look. Well, twice and twice,

00:13:22

probably

00:13:23

an error if we run it. It will be written

00:13:27

01

00:13:32

next. Now I will build different wonderful

00:13:34

interesting

00:13:38

constructions. it will

00:15:25

be pushed

00:15:54

and the question will be

00:15:57

printed.

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